(a) Field of the Invention
The present invention relates to electrostatic filters for cleaning gases comprising electrodes arranged in a housing in order to produce an electric field through which the gas is to be passed for separating the particles from it.
(b) Description of Prior Art
As compared with mechanical filters of porous materials or wire fabric, electrostatic filters have the advantage that the gas passageway through the filter is open at all times and more particularly when such filters are used for cleaning exhaust gases from IC engines no back pressure is produced which interferes with the operation of the engine. The gas flow is caused to pass through an electric field produced by a pair of electrodes and in which the particles contained in the gas are charged and conveyed to a deposit electrode, on which the particles give up their charges however so that they lose their force of attraction and return into the gas current. Therefore a suggestion has been made (see Staub-Reinhalt. Luft 29 (1969) No. 8, August, pages 318 and 319) for the particles to be separated with the aid of electrodes with special trapping properties.
An electrostatic filter with an electrode having trapping properties for IC engines has been proposed in the German patent No. 3,019,991 and its U.S. equivalent U.S. Pat. No. 4,380,990, in which a tubular separating electrode made of perforated sheet metal is placed concentrically around a rod electrode. The exhaust gases are passed through the tube so that the particles conveyed to the separating electrode are entrained with part of the exhaust gas current through the openings of the perforated sheet metal into an external annular space. Finally with this part of the gas current the particles are returned to the IC engine. The overall result is that the particles are trapped and they are prevented from being re-entrained by the main gas current after they have been discharged at the collecting electrode. Such a design is problematical inasfar as the return of soot particles into the IC engine is not possible without supplementary and complex measures needed to prevent rust particles and other sorts of contaminants finding their way from the exhaust pipes into the IC engine with the gases.